Generally speaking, a fuel cell is a device that directly converts the chemical energy in fuel to electric energy by causing an electrochemical reaction between fuel gas, such as hydrogen, and an oxidant agent, such as air, etc. The conversion efficiency is very high, resulting in a wide variety of fuel cell applications, including use as energy supply source for a mobile object equipped with a motor as a drive source.
In order to obtain the desired energy from a fuel cell, it is necessary to supply a sufficient amount of fuel gas and oxidant to the fuel cell. However, when sudden changes in the requested energy occur, the requirement cannot be met due to a delay in the supply means. Therefore, a storage device, such as a secondary cell or a capacitor, is used as a backup supply source in order to compensate for the delay in a mobile object that utilizes a fuel cell.
For the fuel cell to generate power, it is necessary to operate a supply source consisting of fuel gas and an oxidant. In such a system, when the volume of power generation taken from the fuel cell is small, the energy consumed by the system backup device is large compared to the energy generated by the fuel cell, which actually results in a deterioration of the efficiency in obtaining useful energy. Therefore, by using a storage device for a mobile object equipped with a fuel cell, electricity can be supplied from the storage device for inefficient areas in which only a small amount of power is generated and by stopping the supply of the oxidant on the one hand, the chemical reaction that occurs in the fuel cell can be stopped and operation of inefficient areas can also be stopped. (For example, Unexamined Japanese Patent Publication No. 2001-307758 (Page 7, FIG. 5)).